HOUSTON -- The
loss of vital computers governing Russian systems aboard the International Space
Station (ISS) has left the orbital laboratory dependent on U.S. gyroscopes and
NASA?s visiting Atlantis shuttle, and may lengthen the orbiter?s already
extended flight, mission managers said late Wednesday.

The
computers, which control the space station?s Russian-built navigation and
command and control systems, shut down early Wednesday as shuttle astronauts
began retracting
a solar array outside the ISS.

?For
reasons that are unknown to us at this time, we lost both of those computers
and currently we?re in that configuration,? said Mike Suffredini, NASA?s ISS
program manager, during a briefing here at the space agency?s Johnson Space
Center.

The
computer failures have left the station without the use of its Russian attitude
control thrusters, Elektron oxygen generator and other support equipment,
though the ISS has plenty of oxygen supplies and U.S.-built redundancy to make
up for the loss for the time being, Suffredini said.

The station?s
three-astronaut crew and seven visiting shuttle astronauts are not at risk, and
have not lost all vital systems, he added.

?The
lights, the fans and, thank God, the potty, all those things are working,?
Suffredini said.

Shuttle mission
extension possible

The ISS is
currently relying on its four U.S. control moment gyroscopes to maintain its
orientation in space, then shifting to thrusters aboard NASA?s shuttle Atlantis
when the gyroscopes are overwhelmed, or saturated.

That
dependency is leading mission managers to discuss the possibility of extending Atlantis?
13-day mission by a day or so and conserving its supplies where possible,
Suffredini said. Atlantis? mission was already extended
two days to allow an added spacewalk and the repair of a torn shuttle blanket.

In a
worst-case scenario, in which the issue runs beyond current shuttle mission and
exceeds the capabilities of the station?s ?U.S. system ability to control the ISS,
its three-astronaut crew could return to Earth.

?If we are
in that position, we do have the option to depart,? Suffredini said, stressing
that he believes the computer issue will be solved in the next few days. ?I?m not
thinking is something that we will not recover from.?

Computer
issues

The station?s
Russian segment has a network of six primary computers, three for guidance and
navigation and three for command and control, any one of which can handle the
duties of its counterparts, Suffredini said, adding that only two were online
early Wednesday.

While the
computers have experienced hiccups in the past, a system-wide reboot typically
solved the problem, mission managers said.

?Of course,
what?s unique is that when the system went to reboot itself, it wasn?t able to
do that,? Suffredini said.

ISS
engineers are studying a number of possible explanations for the computer
issues, ranging from electromagnetic interference to the added mass and power
supply delivered in the new S3/S4 trusses and solar arrays, mission managers
said.

Russian
flight controllers plan to dedicate much of Thursday morning, when the ISS
flies over Russian ground stations, to working through the computer issues.

Of primary
concern for ISS flight controllers is the recovery of the Russian attitude
control system, which orients the station using thrusters when the outpost?s
U.S. gyroscopes are overwhelmed.

The system,
Suffredini said, is typically used just after a shuttle docks or undocks from
the ISS to dampen out the change in momentum. It is also used to move the ISS
out of the way of orbital debris, he added.

Kelly Beck,
NASA?s lead ISS flight controller for Atlantis? STS-117 mission, said the
station?s Expedition 15 crew worked closely with Russian flight controllers to
work through the computer glitch.

Russian ISS
flight controllers assured the station?s Expedition 15 that everything was
being done to root out the issue.

?Definitely,
we are going to do everything possible to resolve it,? Russia?s Mission Control
told the ISS crew.